RFID Reader Anti-Collision Protocol with Variable Time Duration to Interrogate Tags

In multi-reader Radio Frequency Identification (RFID) systems, there may be some interference between readers when they operate at the same time. This is called a reader collision, and it can result in incorrect tag identification. Scholars have proposed many anti-collision schemes for readers. The neighbor friendly reader anti-collision (NFRA) protocol offers a round-by-round sequence of commands for the RFID reader network in a centralized manner. Subsequently, an improved NFRA protocol with adaptive interrogation capacity (NFRA-AIC) is developed. Based on the framework of NFRA-AIC, an RFID reader anti-collision protocol with variable time duration is proposed to interrogate more tags. The main contribution is that the random number chosen by a reader is determined by the estimated density of adjacent readers. Therefore, fewer readers are disabled by control signals during competition. By adding ROF release slots, the collision caused by the reverse overriding frame (ROF) signals is further reduced. Simulation results indicate that the performance of this proposed protocol is better than that of compared protocols, namely, NFRA and NFRA-AIC. In particular, this proposed protocol provides the improvement of up to 125% in interrogation efficiency comparison to NFRA-AIC.